Esophageal elastance (Ees) was measured in nine trained dogs before and after pentothal anesthesia. Ees increased with lung volume in various recumbent positions. Ees fell with anesthesia in the prone and lateral postures but not in the supine. Closing volume and capacity was measured in 14 anesthetized dogs Closing capacity (CC) was significantly higher in the supine versus prone and lateral positions. In all postures CC was below functional residual capacity. We plan to relate lung resistance-volume behavior to lung pressure- volume curves when changes in the latter occur with posture change and anesthesia. We will then evaluate mechanisms responsible for the changes in pressure-volume curves. We plan to study the effects of various types of artificial ventilation, including positive end-expiratory pressure, on lung mechanics in awake and anesthetized dogs. Bibliographic reference: Gillespie, D.J. and Hyatt, R.E.: Respiratory Mechanics in the Unanesthetized Dog. J. Appl. Physiol., 36:98, 1974.